Process and apparatus for purifying suspensions of fine magnetizable particles in a liquid



Feb. 21, 1961 c. KRIJGSMA N 2, 72, 0

PROCESS AND APPARATUS FOR PURIFYING SUSPENSIONS OF FINE MAGNETIZABLE PARTICLES IN A LIQUID Filed Aug. 1, 1955 INVENTOR. CENTINUS KRIJGSMAN PROCESS AND APPARATUS FOR PURIFYING SUSPENSIONS OF FINE MAGNETIZABLE PARTICLES IN A LIQUID Centinus Krijgsman, Hoensbroek, Netherlands, assignor to Stamicarbon N.V., Heerleu, Netherlands Filed Aug. 1, 1955, Ser. No. 525,701

Claims priority, application Netherlands Aug. 11, 1954 8 Claims. (Cl. 209-38) The present invention relates to a process and apparatus for purifying suspensions of fine magnetizable particles in a liquid, which suspension is contaminated by particles of non-magnetizable material, in which process the suspension to be purified is separated with the help of a magnetic separator into a fraction rich in magnetizable particles and another poor in such particles, which latter fraction is subjected to a further treatment in order to recover at least part of the magnetizable particles which were left in this fraction.

Such a process is applied in coal and ore washeries, where the raw product is separated into a specifically light and a specifically heavy fraction by means of a suspension of magnetic or ferrosilicon in water. After the separation the suspension contains contaminations in the form of fine particles of the material which was separated, which particles have to be removed before the suspension is returned into the separating apparatus.

To this end the suspension is introduced into a magnetic separator which removes the majority of the mag-,

netizable particles. In the remaining fraction, however, so many magnetizable particles are left that it is necessary to treat it in a second magnetic separator which removes another portion of the magnetizable particles from this fraction.

As the price of a magnetic separator is high, the cost of installation of such a regeneration apparatus is likewise high. Moreover, the efiiciency of the second magnetic separator is low, as the suspension fed into this separator has a low concentration of magnetizable particles. The present invention provides a regenerating apparatus comprising only one magnetic separator, while the loss of magnetizable particles is not greater than that occurring in the conventional apparatus with two magnetic separators.

This is achieved according to the invention in that the fraction poor in magnetizable particles, which comes from the magnetic separator, is fed substantially tangentially onto the concave side of a cylindrically curved screening deck. Such a screening apparatus, which is described in United States patent application Serial No. 475,251, filed December 14, 1954, by Freerk J. Fontein, now Patent 2,916,142, issued December 8, 1959, and is therein referred to by the name of sieve bend, has the advantage that, if the feed velocity is sufficiently high, the material is screened to a grain size considerably smaller than the screen apertures. On account hereof, the fine magnetizabe particles will pass through the openings in the screening deck together with the liquid, whereas the coarser, non-magnetizable particles are removed over the screening deck.

The invention will be further explained With reference to the embodiment represented in the drawing, in which the sole figure is a diagrammatic illustration of a preferred embodiment of the invention.

In said drawing 1. represents a separating apparatus in which raw coal is separated with the help of a magnetite suspension into washed coal and shale. The raw coal to its atent be washed is fed in at A, the resulting coal and shale fractions being discharged from the separator at Band C respectively. Besides, an amount of suspension obtained by rinsing of the separated fractions is discharged in dliute form from the separating apparatus, in' order tobe purified and thickened to the specific gravity required. This type of separating apparatus is well known, and is not a part of the present invention. This suspension is conductive to a sieve bend 3 through a conduit 2. Through the openings in the screening deck flows about 90 percent of the supplied amount of liquid with the fine magnetic particles suspended therein. This suspension is collected in a tank 4 and flows from this tank through a conduit 5 to a thickener 6. It is also possible to use, instead of the sieve bend 3, a thickener or a cyclone classifier for the pretreatment of the suspension.

The overflow from the sieve bend 3 contains the coarser non-magnetizable particles, and moreover about 10 percent of the liquid and the magnetite. At 7 this fraction is fed into a magnetic separator 8. At this concentration the efficiency of a magnetic separator is about 98 percent, so that another 9.8 percent of the magnetite is collected in the tank 9, which amount is subsequently led through a conduit 10 to the thickener 6. The fraction of nonmagnetizable particles collected in tank 11 then contains only 0.2 percent of the magnetic originally present in the suspension. This fraction is tangentially supplied to a sieve bend 13 through a conduit 12. About 90 percent of the liquid With the fine magnetite particles suspended therein passes through the openings in the screening deck, so that another 0.18 percent of the magnetite is collected in the tank 14 provided under the sieve bend. This suspension is returned through a conduit 15 to the starting point of the regenerating apparatus. lf necessary, this fraction may also be introduced into the thickener 6. The overflow fraction coming from the sieve bend 13 contains the coarser non-magnetizable particles and a suspension which contains only 0.02 percent of the magnetite fed into the regenerating apparatus. This fraction is discharged from the circuit at 16.

In the conventional regenerating plant, in which the secondary purification is carried out in a second magnetic separator, the efiiciency of the secondary separation is only about percent owing to the low magnetic concentration, so that 0.04 percent of the magnetite is lost in the waste water. Besides the considerable saving in installation cost the application of the present invention has another advantage consisting in a smaller power consumption, as the cost of electric current is lower and the loss of height is smaller, which involves a lowering of pumping cost.

In order to prevent accumulation of fine impurities in the circuit, part of the liquid is drained. As the amount of liquid leaving the circuit at 16 is comparatively small, part of the overflow from the thickener 6 is drained. This overflow is practically free of magnetite. By preference at least part of this liquid is supplied through a conduit 17 to the inlet of sieve bend 13, so that this apparatus receives a sufiicient amount of liquid to be capable of giving the desired screening efiiciency. Furthermore it is possible to drain another portion of the overflow from the thickener at 18.

Through a conduit 19 the thickened suspension is returned to the separating apparatus, as is part of the overflow from the thickener, which returns through the conduit 20 and serves for rinsing the separated coal and shale fractions.

I claim:

1. A process for purifying suspensions of fine magnetizable particles in liquid, which suspensions are contaminated by coarser particles of non-magnetizable materials, which comprises the steps of pretreating the suspension to obtain an undersize fraction containing a major portion of the liquid and magnetizable particles and an oversize fraction containing the remaining liquid and magnetizable particles and the coarser particles of non-magnetizable materials, subjecting the oversize fraction to magnetic separation to obtain a first fraction containing a major portion of the remaining magnetizable particles and a second fraction containing the coarser particles of non-magnetizable materials and the remain ing magnetizable particles in said oversize fraction and then feeding said second fraction to a sieve bend to sep-- arate a major portion of the magnetizable particles therefrom.

' 2. A process as defined in claim 1 wherein said suspension is pretreated by feeding the same to a sieve bend to obtain said undersize and oversize fractions. 3. A process as defined in claim 2 wherein the major portion of the magnetizable particles separated by feeding said second fraction to a sieve bend is combined with the suspension and fed with the suspension to the sieve bend to obtain said undersize and oversize fraction.

4. A process as defined in claim 1 wherein the undersize fraction obtained by pretreating the suspension and the first fraction obtained by subjecting the oversize fraction to magnetic separationare combined and thickened in a thickener.

5. A process as defined in claim 4 wherein at least a part of the overflow from the thickener is fed along with said second fraction to said sieve bend.

6. Apparatus for purifying suspensions of fine magnetizable particles in liquid which suspensions are con taminated by coarser particles of non-magnetizable materials comprising means for pretreating the suspension to obtain an undersize fraction containing a major portion of the liquid and magnetizable particles and an oversize fraction containing the remaining liquid and magnetizable particles and the coarser particles of nonmagnetizable materials, a magnetic separator suitable for treatment of a liquid suspension containing magnetizab-le particles to obtain a first fraction containing a major portion of the magnetizable particles and a second fraction containing coarser particles of non-magnetizable materials and the remaining magnetizable particles, means for conveying the oversize fraction obtainedfrorn said pretreating means to said magnetic separator, a sieve bend, and means for conveying the second fraction obtained from said magnetic separator therefrom and feeding said second fraction to said sieve bend to thereby obtain an overflow fraction and an underflow fraction containingamajor portion of magnetizable particles.

7. Apparatus as defined in claim 6 wherein said pretreating means comprises a sieve bend.

8. Apparatus as defined in claim 6 including conduit means for receiving the underflow fraction from said sieve bend and recirculating the latter to said pretreating means.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Taggert, Arthur F.: Handbook of Mineral Dressing, Wiley, 1945, page 7-06. 

